One of the anti-government protesters during a rally outside a government office where Prime Minster Yingluck Shinawatra had been holding a meeting in Bangkok on Monday, Feb 3, 2014. A group of fast-moving protesters would be dispatched on Tuesday to lay siege to Ms Yingluck's residence as well as state agencies that remain in operation, protest leader Suthep Thaugsuban said. -- PHOTO: REUTERS

BANGKOK (AFP) - Thailand's opposition is set on Tuesday to demand the annulment of last weekend's election and the dissolution of the ruling party, in a legal offensive that threatens to intensify the kingdom's political agony.

Prime Minister Yingluck Shinawatra called Sunday's snap election in a bid to defuse mass rallies that have dogged her government for three months, sparked deadly violence in Bangkok and thrust the kingdom into prolonged political turmoil.

The latest legal move by the opposition, which plans to file a legal challenge to the polls in the Constitutional Court later on Tuesday, came as the United States warned against any moves to stage a military coup, in the most outspoken remarks yet by a major ally.

"We certainly do not want to see a coup or violence," US State Department spokeswoman Jen Psaki said after opposition protesters prevented voting at thousands of polling stations on Sunday, prompting election authorities to withhold results until ballots are cast in all constituencies.

A lawyer for the opposition Democrat Party said their complaint to the Constitutional Court will pivot on a state of emergency, announced in the run-up to polls because of worries over political violence after a spate of gun fights and grenade attacks at protest sites.

The Democrats claim the decree also sought to muzzle critical media and promote pro-government news outlets, breaching the constitution.

"This meant the election was not free and fair," Mr Virat Kalayasiri told AFP late on Tuesday.

"We also seek the dissolution of Puea Thai (ruling party) and a political ban for its executives," Mr Virat said, accusing the government of also acting unconstitutionally by using the emergency decree to seek power.

Thailand's interventionist courts have been closely watched for signs they may enact a "judicial coup" to topple the government.

The country's bitter polarisation hinges on the influence of Ms Yingluck's older brother Thaksin, who lives in self-imposed exile yet draws adoration by the rural northern poor but is loathed by the Bangkok middle class and southerners.

The billionaire-turned-politician and his allies have won every election since emerging onto Thailand's political stage more than a decade ago.

But he was deposed in a military coup soon after his second electoral win in 2006 and two elected Thaksin-backed parties were subsequently dissolved by the courts.

Ms Yingluck's government now faces a slew of legal challenges, including over alleged corruption linked to a controversial rice subsidy scheme and an effort to remodel the make-up of Thailand's senate to make it fully elected.

"It's a political game to discredit Puea Thai and Yingluck's government," said party spokesman Pormpong Nopparit, adding the use of the emergency law was legitimate.

Observers say Thailand's powerful army is reluctant to step in this time, despite calls from anti-government protesters for it to resolve the crisis.

"We remain concerned that political tensions in Thailand are posing challenges to the democratic institutions and processes of Thailand," Ms Psaki told reporters.

Some 10,000 polling stations were unable to open on Sunday, affecting several million people, mainly in Democrat strongholds in Bangkok and the south.

But Puea Thai have hailed Sunday's election as a victory for Thai democracy after ballots were cast by nearly half of those voters whose local polling stations did not close.

Ms Yingluck will remain in a caretaker role with limited power over government policy until elections are held in enough constituencies to have a quorum in parliament.

The protesters on Bangkok's streets want her ousted and her government replaced by an unelected "People's Council" to enact vaguely-defined reforms before new elections.